1. Field of the Invention
The present invention relates to an electrostatic charge image developing toner and a production process for the same, the electrostatic charge image developing toner used for developing an electrostatic image formed on a photosensitive member provided in an image forming apparatus such as copiers and printers. More particularly, the invention relates to an electrostatic charge image developing toner which includes core particles containing at least a resin and a colorant and coated with a resin coating layer, and to a process for producing the same.
2. Description of the Related Art
The image forming apparatuses such as copiers and printers have conventionally used electrostatic charge image developing toners for developing an electrostatic image formed on the photosensitive member.
A milling process is widely used for producing such an electrostatic charge image developing toner. The process includes the steps of: admixing additives including a colorant, a wax and the like to a resin; melting the mixture by heating and kneading the molten mixture; cooling the kneaded product; and milling the product into toner particles of a predetermined particle size.
Unfortunately, in a case where the electrostatic charge image developing toner is produced by the milling process, the produced electrostatic charge image developing toner has various problems such as great variations of particle size, poor productivity, and high production costs. In a case where a toner of a small particle size is produced, in particular, a yield is seriously decreased.
More recently, therefore, an emulsion polymerization/flocculation method has been proposed as a production method of an electrostatic charge image developing toner which allows for arbitrary control of the toner particle configuration or of toner particle size distribution.
Where the electrostatic charge image developing toner is produced by the aforesaid emulsion polymerization/flocculation method, the following procedure may be taken. A dispersion of resin particles is prepared by emulsion polymerization. On the other hand, a dispersion of colorant particles is prepared, while a dispersion of wax to be used as a release agent is prepared. These dispersions are blended together and stirred while a suitable flocculating agent such as an inorganic metal salt is added to the dispersion mixture so as to allow the above resin particles, colorant particles and such to flocculate together. Subsequently, the resultant flocculate is fusion-bonded by heating and thus is produced the toner.
Where the electrostatic charge image developing toner is produced in this manner, however, the colorant or the wax and such is not dispersed equally, then, the colorant, the wax and such are flocculated and exposed to the toner surface, resulting that the toner is lowered in fixing performance and stability to environment. Hence, the toner is varied in electric charge due to the environmental changes, so that formed images may suffer density variations or fogging. Furthermore, in the case of color image formation, formed images may suffer color tone changes.
More recently, there have been proposed an electrostatic charge image developing toner prepared by depositing or fixing resin fine particles to particle aggregates containing at least polymer primary particles and a coloring agent wherein the polymer primary particles contain wax (Japanese Unexamined Patent Publication No. 2002-82487) and a toner wherein surface of pigment dispersion dispersed between main resins is coated with a resin coating layer having a charge control agent dissolved and the pigment dispersion contains wax (Japanese Unexamined Patent Publication No. 2002-82490).
The aforesaid toners can prevent the wax from being exposed to the surface thereof, however, on the other hand, the toners still have a problem that a fine dispersion of the wax therein is difficult and therefore, improvements in fixing performance can not be accomplished sufficiently.